To delete a file, right click on it in the file browser within the side panel. You will be asked either to confirm the deletion or to cancel the process, if you have the right permissions for it.
Be cautious with this feature, there is no easy way to recover the deleted file.
Mac OS X users: this command is not equivalent to putting the file in the trash, but to using the rm command, so that, apart using a specialized commercial tool, you cannot recover the file.
Combining this feature with the Show hidden files feature accessible via the contextual menu of the Filebrowser side panel allows you to delete hidden files more easily than via the rm tool on some systems.
Combining it with the Rename feature accessible via the contextual menu of the Filebrowser side panel allows you to delete an original file once you have edited a new file based on the former one, and to give the new file the same name as the original one.
The first safe usage I can find for this feature is, for example, to remove the backup
A second usage would be, for example, to save a po file again under its original name after updating it via a shell script under a new name, and editing it manually.